Capacitor Questions


(a) Define the capacitance of a capacitor.

(2 marks)

(b) The circuit shown below contains a battery, a resistor, a capacitor and a switch.

The switch in the circuit is closed at time t = 0. The graph shows how the charge Q
stored by the capacitor varies with t.


(i) When the capacitor is fully charged, the charge stored is 13.2μC. The electromotive force (emf) of the battery is 6.0V. Determine the capacitance of the capacitor.

(3 marks)

(ii) The time constant for this circuit is the time taken for the charge stored to increase from 0 to 63% of its final value. Use the graph to find the time constant in milliseconds.

(2 marks)

(iii) Hence calculate the resistance of the resistor.

(1 mark)

(iv) What physical quantity is represented by the gradient of the graph?

(1 mark)


(i) Calculate the maximum value of the current, in mA, in this circuit during the charging process.

(1 mark)

(ii) Sketch a graph on the outline axes below to show how the current varies with time as the capacitor is charged. Mark the maximum value of the current on your graph.

(2 marks)

(Total 12 marks)